The problem you are having is not with the primer. You don't need to sand between coats of paint...I have no idea where this came from. You also don't need to sand between coats of clear...not sure where that started either (etex or devcon). Paint, let dry overnight, then clear. If you are in a hurry, have a hairdryer handy and run it on low between coats. Watch the paint, when it goes from shiny to a dull color it's dry enough for the next coat. Water-based paints can be harder to spray and they dry slower but they are easier to clean up and safer to use.
Jed V.